Actually, you can make use of Custom Properties aka CSS variables.
Firstly, define the button CSS styles
/* button.css */
#buttonRef {
--fontSize: 16px;
font-size: var(--fontSize)
}
The overall flow would be something like the following one e.g
methods: {
changeButtonSize: function(size, event) {
event.preventDefault();
/* size might be either of 's', 'm', 'l' */
/* let the button ref is stored in refs */
const buttonRef = this.$refs[“buttonRef”];
let fontSize = 16;
switch(size) {
case 's':
fontSize = 12;
case 'm':
fontSize = 18;
case 'l':
fontSize = 22;
}
/* dynamically change the value for custom property */
buttonRef.style.setProperty("--fontSize", fontSize);
}
}